1. Field of the Invention
The present invention is related to an efficient Cartesian transmitter, and more specifically an efficient Cartesian transmitter using signal combiner.
2. Description of the Related Art
A conventional transmitter 100 is shown, for example, in FIG. 1. The conventional transmitter 100 can include, for example, a baseband 102, a digital-to-analog converter (DAC) 104, a DAC 106, an upconverter 108, an upconverter 110, an oscillator 112, a combiner 114, a filter 116, and a power amplifier 118. The baseband 102 would transmit, for example, an in-phase signal to the DAC 104 and a quadrature-phase signal to the DAC 106. The upconverter 108 would upconvert the in-phase signal using the oscillator 112 while the upconverter 110 would upconvert the quadrature-phase signal using the oscillator 112. The resulting upconverted signals would be combined by the combiner 114 and output to the filter 116. In one embodiment, the combiner 114 can be part of a Wilkinson linear power combiner, or it can be just a voltage or current summation at an output of the mixers. The filter 116 will output a filtered signal to the power amplifier 118. While the transmitter 100 demonstrated linear power amplification of in-phase and quadrature-phase signals, the transmitter dictated power amplifier operation in back-off mode. This results in considerable amounts of energy being wasted.
A conventional transmitter 200 is shown, for example, in FIG. 2. The conventional transmitter 200 also utilizes linear or saturated amplification of in-phase and quadrature-phase signals. The difference being that in the conventional transmitter 200, the power amplifiers are now utilized prior to the combination of the upconverted signals as shown by the inclusion and placement of the power amplifiers 220 and 222. However, with twice as many power amplifiers, more power may be consumed in the conventional transmitter 200 than in the conventional transmitter 100. For example, the use of the Wilkinson combiner may be inefficient when both the power amplifiers 220 and 222 are active. In such a case, half of the power may be wasted in the combiner 114 as heat in the resistor. In addition, such architecture of the conventional transmitter 200 may require twice as much area as the conventional transmitter 100.
A conventional transmitter 300 is shown, for example, in FIG. 3. In FIG. 3, the conventional transmitter 300 is a polar direct conversion Cartesian transmitter. Thus, instead of using Cartesian components, the conventional transmitter 300 utilizes polar components such as amplitude and phase. However, it still utilizes multiple power amplifiers as seen in the power amplifiers 220 and 222. Again, this consumes excess power and the use of the Wilkinson combiner is also inefficient.
A conventional transmitter 400 is shown, for example, in FIG. 4. In FIG. 4, the conventional transmitter 400 utilizes band-pass DACs 404 and 406 instead of the DACs 104 and 106 in the conventional transmitter 100. However, the summation provided by the combiner 114 can be inefficient if the Wilkinson combiner is used.
Thus, there is a need for an efficient Cartesian transmitter, and more specifically an efficient Cartesian transmitter using signal combiner.